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TLP Library II
22: Introduction to Semiconductors
22.8: Metal–Semiconductor Junction – Rectifying Contact

22.8: Metal–Semiconductor Junction – Rectifying Contact

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Before discussing the behaviour of a metal-semiconductor boundary, it is first necessary to introduce the concept of the work function. The work function of a material is the energy required to remove an electron from the level of the chemical potential and give it enough energy to escape to infinity and arrive there with zero energy.

Albert Einstein first proposed the concept of the work function in his work on the photoelectric effect in metals. It was for this work, rather than for his work on relativity, that Einstein was awarded the Nobel prize in 1921.

When a metal and a semiconductor are joined, two possible types of contact can result, depending on the combination of metal and semiconductor used. The contact may be rectifying, which only allows current to pass in one direction. Alternatively, it could be ohmic, in which case current can pass in either direction. Here we will discuss the rectifying contact, sometimes called the Schottky barrier contact.

The schematic below shows a metal and an n-type semiconductor. The work functions of the metal and semiconductor have been labelled Φ_M and Φ_S respectively. The dashed line at the top represents the zero of energy at infinity.